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A clash among members of a famous galaxy quintet reveals an assortment of stars across a wide color range, from young, blue stars to aging, red stars. This portrait of Stephan's Quintet was taken by the Wide Field Camera 3 (WFC3) aboard NASA's Hubble Space Telescope.
Stephan's Quintet, as the name implies, is a group of five galaxies. The name, however, is a bit of a misnomer. Studies have shown that the group member at upper left is actually a foreground galaxy about seven times closer to Earth than the rest of the group. Three of the galaxies have distorted shapes, elongated spiral arms, and long, gaseous tidal tails containing many star clusters, proof of their close encounters. These interactions have sparked a frenzy of star birth in the central pair of galaxies. This drama is being played out against a rich backdrop of faraway galaxies.
NGC 7319, at top right, is a barred spiral with distinct spiral arms that follow nearly 180 degrees back to the bar. The blue specks in the spiral arm at the top of NGC 7319 and the red dots just above and to the right of the core are clusters of many thousands of stars. Most of the quintet is too far away even for Hubble to resolve individual stars.
Continuing clockwise, the next galaxy appears to have two cores, but it is actually two galaxies, NGC 7318A and NGC 7318B. Encircling the galaxies are young, bright blue star clusters and pinkish clouds of glowing hydrogen where infant stars are being born. These stars are less than 10 million years old. Far away from the galaxies, at right, is a patch of intergalactic space where many star clusters are forming.
The galaxy at bottom left, NGC 7317, is a normal-looking elliptical galaxy that is less affected by the interactions.
Sharply contrasting with these galaxies is the dwarf galaxy NGC 7320 at upper left. Bursts of star formation are occurring in the galaxy's disk, as seen by the blue and pink dots. In this galaxy, Hubble can resolve individual stars, evidence that NGC 7320 is closer to Earth.
NGC 7320 is 40 million light-years from Earth. The other members of the quintet reside 290 million light-years away in the constellation Pegasus. These farther members are markedly redder than the foreground galaxy, suggesting that older stars reside in their cores. The stars' light also may be further reddened by dust stirred up in the encounters.
Spied by Edouard M. Stephan in 1877, Stephan's Quintet is the first compact group ever discovered.
This Hubble observation was part of the Hubble Servicing Mission 4 Early Release Observations. NASA astronauts installed the WFC3 camera during a servicing mission in May, 2009 to upgrade and repair the Hubble telescope, which was 19 years old at the time.